Osteoarthritis is the most common form of arthritis, and is thought to be from the inevitable wear and tear of aging. Scientists recently identified large numbers mast cells in the synovial fluid of osteoarthritic joints; and suggested IgE-mediated mast-cell activation promoted inflammation and cartilage destruction, in osteoarthritis.
Mast cells are the first immune cells to attack an infectious pathogen. Mast cells signal the immune system to start a specific sequence of attacks, by other types of immune cells (histamine and tryptase may be the mast-cell signal), which ends with plasma cells creating IgE antibodies. The presence of large numbers of mast cells in the synovial fluid of osteoarthritic joints supports an immune system attack against a pathogen, and that osteoarthritis is another form of inflammatory
arthritis/autoimmune disease, which has an infectious origin.